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Personally, I think the real reason people keep insisting MDZS is told from WWX's POV, even though they admit it's third person omniscient, is because JC is addressed by his birth name 'Jiang Cheng' throughout the entire novel and not his courtesy name. So people wrongly assume it must be from WWX's perspective...
Well, those that cling to such a take aren't going to like the real answer to this... But that's still not the case. If it were from WWX's perspective, JYL would be addressed as 'Shijie', LWJ would be 'Lan Zhan' and JFM would be 'Jiang-shushu' etc. JC is addressed by his birth name throughout the novel because even the narrator thinks he is a clown.
Sorry, but that's the reason. They do not think he deserves respect, just as the rest of the cultivation world doesn't either. If you actually look at the text, you'll notice behind his back, nearly everyone calls JC by his birth name out of disrespect - it's literally in the first few chapters for all to see. He's rarely called by his courtesy name by anyone other than LWJ, WWX when he's pissed and later by JGY and XY in the extras. That's it. It's a show of disrespect throughout the novel and the narrator shows the same. JC isn't called 'Sandu Shengshou' for nothing you know, it's a running theme of disrespect for a character that doesn't deserve much if any at all.